1. Field of the Invention
The present invention generally relates to an air conditioner and, more particularly, to an inverter controlled air conditioner with an over current detection.
2. Description of the Related Art
As is generally known, a conventional inverter controlled air conditioner includes an inverter drive section for supplying a V/F pattern output having a predetermined voltage and frequency corresponding to an air conditioning load from an inverter section to a variable-capacity compressor. The variable-capacity compressor can vary a capacity of circulating a refrigerant in a refrigeration cycle including external and internal heat-exchangers. The inverter drive section supplies a V/F pattern output having a low voltage and frequency to the variable-capacity compressor through the inverter section when a capacity required by the air conditioning load is low. In contrast to this, when a capacity required by the air conditioning load is high, the inverter drive section supplies a V/F pattern output having a high voltage and frequency.
In the above-mentioned inverter controlled air conditioner, assume that it is difficult to start the compressor due to a dead refrigerant (dissolved in a lubricating oil in the compressor) or a load of the refrigeration cycle, the compressor is locked, or the inverter section fails. In such a case, an over current is supplied to the inverter section. Therefore, an inverter controlled air conditioner, having a function for causing an over current detection section to detect the over current supplied to the inverter section, and causing the inverter drive section to protect the inverter section and equipments which constitute the refrigeration cycle, is conventionally used.
If the inverter drive section determines the presence of an abnormality upon only one detection of an over current, a determination error may occur. In order to prevent such an error, the inverter drive section conventionally executes an over current protection routine shown in a flow chart in FIG. 7. More specifically, as indicated by a solid line in FIG. 7, it is determined whether there is an input from the over current detector in step S1. If YES in step S1, the compressor is temporarily stopped (step S2). The number of inputs from the over current detector is counted to determine a predetermined count N =Nend (steps S3 and S4). When the input count from the over current detector reaches a predetermined count, i.e., N =Nend, an abnormality is determined, and the compressor is perfectly stopped (steps S5 and S6). When NO in step S4, i.e., the input count does not reach the predetermined count Nend, the compressor is restarted (step S7).
The above-mentioned control operation can be performed when the compressor is locked or the inverter section is failed. However, when it is difficult to start the compressor due to dissolution of the refrigerant or a load of the refrigeration cycle, the compressor may restart by itself. Therefore, if it is determined that an abnormality occurs and the compressor is perfectly stopped, inconveniences may occur.
As indicated by a broken line in FIG. 7, the air conditioner, in which the number of inputs from the over current detector is counted, a voltage and frequency supplied to the compressor are set to be a reference V/F pattern if N&lt;N.sub.2, i.e., YES in step S8, and the voltage and frequency supplied to the compressor are set to be a (reference--1 step) V/F pattern if NO in step S8, thus restarting the compressor (steps S9, S10, and S11), is also conventionally used.
In this case, however, the V/F pattern is varied in accordance with the number of inputs supplied from the over current detector again, as shown in FIG. 8. Therefore, characteristics of the over current as a function of time vary between time t1 and t2, and hence it is difficult to determine without an error whether an abnormality occurs in the inverter section or the compressor is locked, i.e., A or B.
As described above, the conventional inverter controlled air conditioner has the following drawback. Even if a starting operation is temporarily failed due to a variation in load of the refrigeration cycle, the compressor may be perfectly stopped, or a determination error of the abnormality in the inverter section or the compressor may occur. As a result, abnormality contents cannot be determined with reliability.